The present invention relates to two-coordinate length measuring devices for microscopic instruments, particularly microhardness and small load hardness-testers.
Microhardness testers in which measurements in two coordinates are possible and in which, for example, the length of both diagonals of a hardness impression can be determined, are known. With conventional apparatus for the measurement of the diagonals of an object, the measuring ocular is mounted in a rotatable manner. The reference mark or marks are also mounted so that they are displaceable in the direction of the diagonals of the impression. This is true both for marks which consist of straight lines or only a single straight line, and those that are constructed in the form of a 90.degree. angle in order to accommodate the rectangular shape of the impression. In the measurements of the diagonals of the impression, the foregoing marks are moved into superposition with the edges or corners of the impression. While in the case of angular marks, the impression is "encompassed" and therefore emphasis is on area measurements, the devices of the type utilizing straight lines as marks insure exact superposition on the corners and thus better determinations of length. However, in apparatus using either type of mark, as mentioned above, following the measurement of one of the diagonals, rotation of the ocular containing the mark by 90.degree. is necessary in order to determine the length of the second diagonal.